在另一個trait的trait實作中使用constgeneric會導致“不受約束的const引數”錯誤

我正在嘗試實作一些抽象的線性代數特征和結構，作為我學習 Rust 實踐的一部分。在當我執行下面的代碼VectorAbstract<TValue>為VectorDynamic<TValue>沒有任何問題; 但是當我嘗試做同樣的事情時，VectorStatic<TValue, DIM_COUNT>我收到以下錯誤：

the const parameter `DIM_COUNT` is not constrained by the impl trait, self type, or predicates
unconstrained const parameter
note: expressions using a const parameter must map each value to a distinct output value
note: proving the result of expressions other than the parameter are unique is not supported

我在這里做錯了什么？
實作這一點的正確方法是什么？
這是我的代碼：

pub trait VectorAbstract<TValue: Scalar>: VectorSpaceElement   // a dozen std traits
{
    fn dot(lhs: &Self, rhs: &Self) -> TValue;
}

pub trait VectorDynamic<TValue: Scalar>: VectorAbstract<TValue> {
    fn dim_count(&self) -> usize;
    fn from_list(arr: Vec<TValue>) -> Self;
}

pub trait VectorStatic<TValue: Scalar, const DIM_COUNT: usize>: VectorAbstract<TValue> {
    fn from_array(arr: [TValue; DIM_COUNT]) -> Self;
}

impl<TValue: Scalar, TVector: VectorDynamic<TValue>> VectorAbstract<TValue> for TVector {
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        // ... dot product body for dynamic vectors ...
    }
}

impl<TValue: Scalar, const DIM_COUNT: usize, TVector: VectorStatic<TValue, DIM_COUNT>>
    VectorAbstract<TValue> for TVector
{
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        // ... dot product body for static vectors ...
    }
}

更新 1

我還嘗試了以下方法：

pub trait VectorStatic<TValue: Scalar>: VectorAbstract<TValue> {
    const DIM_COUNT: usize;
    fn from_array(arr: [TValue; Self::DIM_COUNT]) -> Self;
}
impl<TValue: Scalar, TVector: VectorStatic<TValue>> VectorAbstract<TValue> for TVector {
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        // ... dot product body for static vectors ...
    }
}

但是我在宣告from_array函式時收到以下錯誤：

generic parameters may not be used in const operations  
cannot perform const operation using `Self`  
note: type parameters may not be used in const expressions  

注意：我希望在編譯時以某種方式獲得 DIM_COUNT，所以沒有fn dim_count()for VectorStatic.

更新 2

Also when I completely remove the implementation for VectorStatic, I get another error in another file where I have a Vector2 struct and try to implement VectorStatic<TValue, 2> for that:

pub struct Vector2<TValue: Scalar> {
    pub x: TValue,
    pub y: TValue,
}
impl<TValue: Scalar> VectorStatic<TValue, 2> for Vector2<TValue> {
    // ... implementation ...
}

And here's the error :

the trait bound `math::algebra::vectors::vector2::Vector2<TValue>: math::algebra::abstractions::VectorDynamic<TValue>` is not satisfied
the trait `math::algebra::abstractions::VectorDynamic<TValue>` is not implemented for `math::algebra::vectors::vector2::Vector2<TValue>`

Note that this Vector2 struct is not supposed to be a VectorDynamic at all. There's definitely something I have not understood clearly here, maybe rust thinks I'm trying to make every VectorAbstract a VectorDynamic or something like that ?
What is it that I'm missing ?

UPDATE 3

Perhaps I should also mention that I already tried the following :

impl<TValue: Scalar> VectorAbstract<TValue> for dyn VectorDynamic<TValue>
{
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        // ... dot product body for dynamic vectors ...
    }
}
impl<TValue: Scalar, const DIM_COUNT: usize> VectorAbstract<TValue> for dyn VectorStatic<TValue, DIM_COUNT>
{
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        // ... dot product body for static vectors ...
    }
}

But in that case I get this error for both :

the trait `math::algebra::abstractions::VectorDynamic/VectorStatic` cannot be made into an object

and then a dozen lines that say because they used Self as a type parameter.

uj5u.com熱心網友回復：

您的原始代碼的問題在于，不能保證型別TVector只會實作VectorStatic<TValue, 1>而不是實作VectorStatic<TValue, 2>會產生沖突的VectorAbstract<TValue>.

更新 1 是要走的路，因為這樣一個型別不能實作VectorStatic多次。目前這需要每晚生銹，#![feature(generic_const_exprs)]并在lib.rs/開始時添加main.rs

接下來的問題將是2impl的-s VectorAbstract<TValue>。同樣，沒有什么可以保證TVector不實作兩者VectorDynamic<TValue>并且VectorStatic<TValue>會導致VectorAbstarct<TValue>. 據我所知，即使功能不穩定，也無法做到這一點。最好的方法是使用包裝結構。

VectorStatic1 VectorStaticWrapper1需要添加的功能，并且僅適用于夜間 Rust 版本，VectorStatic2 VectorStaticWrapper2可以穩定運行。

#![feature(generic_const_exprs)]

pub trait Scalar {}

pub trait VectorAbstract<TValue: Scalar>: 
{
    fn dot(lhs: &Self, rhs: &Self) -> TValue;
}

pub trait VectorDynamic<TValue: Scalar>: VectorAbstract<TValue> {
    fn dim_count(&self) -> usize;
    fn from_list(arr: Vec<TValue>) -> Self;
}

pub trait VectorStatic1<TValue: Scalar>: VectorAbstract<TValue> {
    const DIM_COUNT: usize;
    fn from_array(arr: [TValue; Self::DIM_COUNT]) -> Self;
}

pub trait VectorStatic2<TValue: Scalar, const DIM_COUNT: usize>: VectorAbstract<TValue> {
    fn from_array(arr: [TValue; DIM_COUNT]) -> Self;
}

struct VectorDynamicWrapper<T>(T);
struct VectorStaticWrapper1<T>(T);
struct VectorStaticWrapper2<T, const DIM_COUNT: usize>(T);

impl<TValue: Scalar, TVector: VectorDynamic<TValue>> VectorAbstract<TValue> for VectorDynamicWrapper<TVector> {
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        let lhs = &lhs.0;
        let rhs = &rhs.0;
        todo!()
    }
}

impl<TValue: Scalar, TVector: VectorStatic1<TValue>>
    VectorAbstract<TValue> for VectorStaticWrapper1<TVector>
{
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        let lhs = &lhs.0;
        let rhs = &rhs.0;
        let dim_count = TVector::DIM_COUNT;
        todo!()
    }
}

impl<TValue: Scalar, const DIM_COUNT: usize, TVector: VectorStatic2<TValue, DIM_COUNT>>
    VectorAbstract<TValue> for VectorStaticWrapper2<TVector, DIM_COUNT>
{
    fn dot(lhs: &Self, rhs: &Self) -> TValue {
        let lhs = &lhs.0;
        let rhs = &rhs.0;
        todo!()
    }
}

標籤：generics rust

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